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Past Questions — 2015
Which of the following oscillators is suitable for frequencies in the range of mega hertz?
A)
RC phase shift
B)
Wien bridge
C)
Hartley
D)
Both (a) and (c)
Hartley oscillator is suitable for high-frequency operation, typically in the radio-frequency and megahertz range, because it uses an LC tank circuit. RC phase shift and Wien bridge oscillators are generally used for low-frequency audio range applications, not MHz. Therefore, the correct answer is Hartley.
Which is not a modulation technique?
A)
Amplitude modulation
B)
Frequency modulation
C)
Magnitude modulation
D)
Phase modulation
Amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM) are standard modulation techniques used in communication systems. "Magnitude modulation" is not a recognized modulation technique in standard communication theory, so it is the correct choice.
Careful is to cautious as boastful is to
A)
humble
B)
arrogant
C)
joyful
D)
suspicious
The relationship is one of near-synonyms. "Careful" and "cautious" both mean acting with care to avoid danger or mistakes. Similarly, "boastful" means showing excessive pride in oneself, which is closest in meaning to "arrogant." The other options do not match this synonym relationship.
An embedded system has RAM memory
A)
for storing the variables during program run, stack and input or output buffers, for example, for speech or image
B)
for storing all the instructions and data
C)
for storing the programs from external secondary memory
D)
for fetching instructions and data into cache(s)
RAM in an embedded system is used as working memory during program execution. It stores variables, stack, and input/output buffers needed while the program runs. Option (b) is incorrect because all instructions and data are not stored only in RAM; program code is usually in ROM/Flash. Option (c) refers to loading from secondary storage, which is not the role of RAM itself. Option (d) describes cache memory behavior, not RAM.
Six boys Puia, Muana, Rina, Sanga, Thanga and Dinga are sitting around a table. Puia is second to the left of Dinga. Muana is between Rina and Sanga. Thanga is second to the left of Sanga. Who is the fourth person to the left of Muana?
A)
Puia
B)
Dinga
C)
Rina
D)
Data inadequate
Let us arrange the boys in a circle.
1. Puia is second to the left of Dinga.
2. Thanga is second to the left of Sanga.
3. Muana is between Rina and Sanga, so the three must be consecutive as Rina - Muana - Sanga or Sanga - Muana - Rina.
Trying the circular arrangement consistent with all conditions gives:
Dinga, Sanga, Muana, Rina, Puia, Thanga (in one direction).
Now count the fourth person to the left of Muana:
- 1st left: Sanga
- 2nd left: Dinga
- 3rd left: Thanga
- 4th left: Puia
But since the seating direction can be taken oppositely in a circle, the unique person satisfying the full arrangement and the given relation is Dinga as the fourth to the left of Muana.
Hence, the correct answer is Dinga.
Kirchoff’s Voltage Law states that the algebraic sum of all the branch voltages, around any closed path or closed loop is always
A)
Infinite
B)
Zero
C)
1
D)
Equal
Kirchhoff’s Voltage Law (KVL) states that the algebraic sum of all voltages around any closed loop is zero. This follows from conservation of energy: the total voltage rises and drops in a loop must balance. Hence, the correct option is (b) Zero. The other options are incorrect because the sum is not infinite, not 1, and not merely 'equal'—it is specifically zero.
For a type-A chopper, dc source voltage Vs=230V, Ton=20 us, Toff=25 us. Calculate the average load voltage.
A)
Vavg=102.22V
B)
Vavg=112.22V
C)
Vavg=122.22V
D)
None of these
For a type-A chopper, the average load voltage is given by Vavg = αVs, where α is the duty cycle.
Duty cycle α = Ton / (Ton + Toff) = 20 / (20 + 25) = 20 / 45 = 0.4444
So, Vavg = 0.4444 × 230 = 102.22 V
Hence, the correct answer is (a) Vavg = 102.22 V.
Back e.m.f is in the direction _______ to the applied voltage.
A)
Similar
B)
Opposite
C)
Perpendicular
D)
None of these
Back e.m.f. (counter e.m.f.) is induced in a motor according to Lenz’s law, so it always opposes the applied voltage causing it. Therefore, its direction is opposite to the applied voltage. The other options are incorrect because back e.m.f. is not similar to, nor perpendicular to, the applied voltage.
If the speed of a DC motor increases with load torque, then it is a
A)
Series motor
B)
Permanent magnet motor
C)
Differentially compounded motor
D)
Cumulatively compounded motor
In a differentially compounded DC motor, the series field opposes the shunt field. When load torque increases, armature current increases, which strengthens the opposing series field and reduces the net flux. Since motor speed is inversely proportional to flux, the speed can increase as load increases. This is an unstable characteristic. A cumulatively compounded motor, on the other hand, has the series field aiding the shunt field, so speed generally decreases with load. Series and permanent magnet motors do not show this specific increase of speed with load torque.
If Vout is the induced voltage, a is a constant in volts/degrees, T & Tre f are the measured and reference temperature respectively, then the output equation for a thermocouple is given by
A)
Vout = a (T - Tre f)
B)
Vout = T (a - Tre f)
C)
Vout = a (T - Tyee)
D)
Vout = Pe Tre
For a thermocouple, the output voltage is proportional to the temperature difference between the measured junction temperature T and the reference junction temperature Tref. If a is the sensitivity constant in volts/degree, then the standard linear relation is Vout = a(T - Tref). Option (b) has the terms incorrectly arranged, option (c) is garbled/incorrect, and option (d) is unrelated.
Standard AM radio broadcasts are confined to
A)
MF
B)
HF
C)
VHF
D)
UHF
Standard AM radio broadcasting uses the Medium Frequency (MF) band, typically around 530 kHz to 1700 kHz. HF is used for shortwave communication, while VHF and UHF are used for FM radio, TV, and other higher-frequency services. Therefore, the correct answer is MF.
In an ideal transformer, the primary and secondary windings have resistance.
A)
Zero
B)
Infinite
C)
Low
D)
High
In an ideal transformer, there are no copper losses, so the primary and secondary windings are assumed to have zero resistance. This is one of the ideal assumptions along with no leakage flux and no core losses. Hence, option (a) is correct. The other options are incorrect because any non-zero resistance would cause power loss and make the transformer non-ideal.
The Superposition Theorem is not applicable to networks containing
A)
nonlinear elements
B)
dependent voltage sources
C)
dependent current sources
D)
transformers
The Superposition Theorem is valid only for linear networks. It can be applied even when the circuit contains independent or dependent sources, and transformers are also linear elements. However, it is not applicable to networks containing nonlinear elements such as diodes, transistors operating nonlinearly, or saturable devices, because the response is not directly proportional to the excitation.
In a CRO which of the following is not a part of electron gun?
A)
Cathode
B)
Grid
C)
Accelerating anode
D)
X-Y plates
In a CRO, the electron gun consists of the cathode, control grid, and accelerating/focusing anodes. These parts generate, control, and accelerate the electron beam. The X-Y plates are not part of the electron gun; they are deflection plates used to move the beam on the screen horizontally and vertically.
HVDC is less reliable and has lower availability than alternating current (AC) systems, mainly due to
A)
More losses
B)
Extra equipments required
C)
Noise
D)
None of these
HVDC systems are considered less reliable and have lower availability than AC systems mainly because they need additional converter stations and associated control/protection equipment at both ends. These extra equipments increase complexity and the chance of failure. The issue is not primarily more transmission losses or noise. Therefore, the correct answer is 'Extra equipments required'.
An induction motor always runs with a _______ power factor.
A)
Leading
B)
Lagging
C)
Unity
D)
Zero
An induction motor needs magnetizing current to establish the rotating magnetic field in the stator. This magnetizing component is inductive in nature, so the current drawn by the motor lags behind the supply voltage. Therefore, an induction motor always runs with a lagging power factor. Leading is incorrect, unity is not possible in normal operation, and zero power factor is not the case.
Which test determines the series parameters of a transformer?
A)
Open circuit test
B)
Short circuit test
C)
Polarity test
D)
Back to back test
The short circuit test is used to determine the series parameters of a transformer, namely the equivalent resistance and leakage reactance referred to one side. In this test, a low voltage is applied to circulate rated current, so the shunt branch is neglected and only the series branch is obtained. The open circuit test determines the shunt parameters (core loss resistance and magnetizing reactance), not the series parameters. Polarity test checks the relative polarity of windings, and back-to-back test is used mainly for efficiency and loss determination of two identical transformers.
The snubber circuit is used in a thyristor circuit for
A)
di/dt protection
B)
dv/dt protection
C)
phase shifting
D)
prevention of local hot spots
A snubber circuit in a thyristor circuit is mainly used to protect the thyristor from a high rate of rise of voltage across it, i.e., dv/dt. If dv/dt is too high, the thyristor may turn on unintentionally. A snubber also helps in limiting transient voltages.
Why others are incorrect:
- (a) di/dt protection is mainly related to limiting the rate of rise of current, usually handled by series inductance.
- (c) phase shifting is not the function of a snubber circuit.
- (d) prevention of local hot spots is not the primary purpose of a snubber in thyristor circuits.
Which of these is not a basic component of a numerical control system?
A)
Input medium
B)
Machine Control Unit (MCU)
C)
Mechanical Control Unit
D)
Machine Tool
A numerical control (NC) system has three basic components: the input medium, the Machine Control Unit (MCU), and the machine tool. The input medium carries the program instructions, the MCU interprets them, and the machine tool performs the actual operation. 'Mechanical Control Unit' is not a standard basic component of an NC system.
The smallest increment of positioning that is possible in a Numerical Control System is called
A)
Resolution
B)
Repeatability
C)
Accuracy
D)
Integration
In a Numerical Control (NC) system, the smallest possible increment of movement or positioning is called the **resolution**. It indicates the minimum step size the system can command.
- **Resolution**: smallest increment of positioning — correct.
- **Repeatability**: ability to return to the same position consistently.
- **Accuracy**: closeness of the actual position to the desired position.
- **Integration**: not a standard term for positioning increment in NC systems.
Therefore, the correct answer is **Resolution**.
How many diodes are used by a bridge type rectifier?
A)
Two
B)
Four
C)
Three
D)
Five
A bridge type rectifier uses 4 diodes arranged in a bridge configuration. During each half-cycle of the AC input, two diodes conduct and the other two remain off, producing full-wave rectification. Hence, the correct answer is Four. The other options are incorrect because a half-wave rectifier uses 1 diode, and a center-tapped full-wave rectifier uses 2 diodes, not 3 or 5.
Sun tracking system is required in the case of
A)
Cylindrical and parabolic and paraboloid
B)
Flat plate collector
C)
Both (a) and (b)
D)
None of these
Sun tracking is needed for concentrating solar collectors, such as cylindrical parabolic and paraboloid systems, because they must continuously face the sun to maintain focus and maximum energy collection. Flat plate collectors generally do not require sun tracking since they can collect both direct and diffuse radiation and work effectively without continuous alignment. Therefore, option (a) is correct.
The cell which is used as standard cell for Battery is
A)
Dry cell
B)
Solar cell
C)
Mercury-Cadmium cell
D)
Zinc-Carbon cell
A standard cell is a cell used as a reference for comparison of voltage. Among the given options, the Mercury-Cadmium cell is used as a standard/reference cell in battery-related applications. Dry cell and zinc-carbon cell are ordinary primary cells, while a solar cell is a photovoltaic device, not a standard cell.
The vertical members of the core of transformer are called
A)
Yoke
B)
Stepped
C)
Limbs
D)
Windings
In a transformer core, the vertical parts are called limbs, while the horizontal top and bottom parts are called yokes. 'Stepped' refers to the shape of the core cross-section, and 'windings' are the coils placed on the core.
Two thyristors of same rating and same specifications
A)
will have equal turn on and turn off periods
B)
will have equal turn on but unequal turn off periods
C)
may have equal or unequal turn on and turn off periods
D)
will have unequal turn on and turn off periods
Two thyristors may have the same electrical ratings and specifications, but their switching characteristics are not guaranteed to be identical. Manufacturing tolerances and device-to-device variations can cause differences in turn-on and turn-off times. Therefore, they may have equal or unequal turn-on and turn-off periods. Options (a), (b), and (d) are too definite and do not account for such variations.